A number of farmers over the last decade, especially those in consistently arable rotations, have discovered problems with matching weed management with increasing pressure to produce crops more efficiently in an increasingly regulated world.
In a similar light to the 2012 floods , weeds such as black-grass (Aloprcurus myosuroides) have topped the agricultural industry’s front pages. There are a number of reasons why black-grass has become such a particular problem. Increasing levels of herbicide resistance to chemical formulas has meant the typical chemicals applied to these weeds does not have the same efficacy that they may have done ten years ago. In addition, increasingly wet weather, consistent cropping and less varied cultivations all have some affect on the build up of black-grass.Despite a particular black-grass problem in one of our fields, other problems that are becoming important on many farms include nitrate leaching over the winter period, loss of soil organic matter over long periods of time due to lack of livestock and more varied rotations. This is where many farmers have turned to cover cropping to counter a number of these issues in certain contexts.
Cover cropping is the idea of growing a crop to cover the ground during fallow periods, whether that is between vegetable rotations or between more common arable rotations. Often the winter period from September till March will have a higher level of rainfall and have more consistent ground saturation, this can lead to leaching of mobile nutrients such as nitrogen. Cover crops can counter this by using that nitrogen in the soil, storing it in the leafy green structure of each plant, allowing it to be returned to the soil and decomposed later in the spring ready for the next crop.
Germinated Mustard seeds
This year we have decided to test some White Mustard as a cover crop and see how it could fit into our farming system on a longer term basis. We drilled the Mustard seeds in early August, straight after the Wheat had been harvested. Fortunately the weather was warm, with plenty of sunshine hours and some rainfall allowing the Mustard to germinate and grow well. During harvesting we usually bale all of the straw from a field for use on the farm for our livestock. However this year we chopped the outside headland of straw and spread it over the ground. We did this to save time when baling the straw and means that all of our straw is better quality due to less green stalks that often lie towards the outside of fields.
This caused a large volume of straw around the outside of the field which hampered the drilling process by blocking the tine drill. This, and the fact that more straw can also allow more food and places for slugs to get to meant that slug poplations round the outside were higher than the rest of the field. It also meant that the Mustard did not germinate and grow as well on the outer headland. Apart from this, the majority of the crop looks healthy and well. It will be interesting to see how it grows until November or December when it will need to be cut down and incorporated into the soil ready for its decomposition.
Mustard after 5 weeks, growing over the mix of wheat and black-grass
This addition of green matter helps to aerate and build up the soils organic matter over a longer period of time, therefore although the Nitrogen benefit is short term, soil structure and organic matter can take many decades to build up appreciably. Cover crops such as Mustard are also helpful, certainly not efficient, in competing against other weeds. Thus by vigorously growing above the weeds, it creates a canopy allowing the weeds to germinate and grow, but with effective management (killing and burying before seeding) can dispose of those germinated weed seeds. White Mustard is also known for its ‘allelopathic’ biochemicals that hinders other seeds from germinating. This is thought to aid the cleaning of the seed bed. This effect can also stop planted seeds from germinating if within 6 weeks of the mustard being incorporated into the soil.
Some other benefits for the crop of White Mustard at the farm are helpful for a number of users within the farm ecosystem. Of course with any benefits, there are also a number of costs involved with growing this extra cover crop that will eventually end up being ploughed in rather than harvested for seed. The seed, the labour and fuel to drill the crop, the fertiliser used to ensure it is established well all comes to a cost. With a suitable rotation though, a cover crop helps to spread the work load between the busy summer and the usually quieter spring time.
Picture showing the problems straw can present to germination around the outside of the field